This invention relates to computer programming, and more particularly to computer aided software development.
The purpose of the invention is to provide a programming environment designed to enhance the speed and productivity of software development, particularly a method for substantially decreasing the time required for recompilation and relinking in the edit-compile-link-run cycle of the software development process. When code is being written, the elapsed time through the edit-compile-link-run cycle after the user makes a small change to the application source code is called the turnaround time. A primary purpose of the invention is to minimize this turnaround time.
The programming "environment" as the term is used herein means the set of programs or modules (i.e., code) used to implement the edit-compile-link-run cycle for a developer, who is ordinarily seated at a terminal and engaged in the endeavor of writing code. The environment which is the subject of this invention will be called "the environment", whereas any program being developed under the environment will be called "an application". The environment is capable of supporting the development of any application, including the environment itself. The user of the environment is called "the developer", while the user of an application is called "the end user".
Software development is characterized by a process involving the steps of editing the program, compiling and linking the program, and running the program. A compiler translates a source program that has been written in a high-level language such as Pascal or Fortran into a machine executable form known as an object program.
The software development process is further divided into stages, with the earlier stages characterized by rapid and large scale activity (e.g., editing) in all or most of the application source files, and in the later stages characterized by less frequent and smaller changes in fewer than all of the source files. During the earlier stages the objective is removing syntax errors in the source code and logic errors in the application. During the final stages the objective is improving the efficiency of the application and testing the behavior of the application in the form it will be delivered to the end user.
It is generally desirable that the quality of the object code generated by a compiler, as measured in terms of efficiency, be as good as possible. A compiler that generates very efficient object code is known as an optimizing compiler. Optimized object code is characterized by maximized efficiency and minimized execution time. However, the complex methods and techniques employed by optimizing compilers to produce highly efficient object code necessarily result in relatively long compile times.
The removal of logic errors is relatively independent of the efficiency of the implementation of the application; therefore, during the early stages of software development, it is desirable that the environment emphasize turnaround time over optimization. In addition, during the early stages it is advantageous to insert application-run-time checks for certain kinds of detectable faults such as boundary overrun. The concerns with efficiency and testing during the final stages require optimization, and the lower frequency of changes makes the use of traditional software tools effective.
The edit-compile-link-run cycle is typically repeated numerous times during development of a particular piece of software. At any stage of this activity the developer may be required to correct detected errors (as used herein, "error" means "need for a change", since the motivation for making a change may be either repairing a previous oversight or adding new functionality). Errors may be detected by the compiler, the linker, or later by the programmer during test execution. This style of interaction in conventional environments results in frequent context changes and delays for the developer. Context changes occur while the developer separately and sequentially invokes the editor, the compiler, the linker, and the application itself. Delays occur while the developer waits for these separate tools to complete their tasks.
Thus, while long compile times are tolerable in the final stages of developing an application, i.e., when generating production quality object code, these delays are not tolerable in the early stages of the process of developing, testing, and debugging software where long compile and link times will be much more noticeable since these are invoked much more often. Moreover, changes in the application code made during development are usually localized and small in size with respect to the rest of the program. In known software development environments, the turnaround time for compiling an application module is proportional to the size of the module and the turnaround time for linking an application is proportional to the size and number of modules. In the environment of this invention both compilation and linking turnaround are proportional to the size of the changes to the source code made by the developer since the last compile/link operation. Many applications programs have 100,000 to 1,000,000 or more lines of code; the turnaround time (time for the edit-compile-link-run loop to complete) in developing such programs can become an overnight activity, and thus presents a major burden.
Thus, it is desirable to provide a software development environment that would allow fast turnaround in the edit-compile-link-run cycle.
Examples of commercially available developmental compilers include "Quick C.TM." by Microsoft Corporation, "LightSpeed C" by Symantek Corporation, "Turbo C" by Borland Corporation, and Saber-C by the Saber Company. These prior systems are faster than traditional batch compilers, and may provide some degree of incremental (as distinguished from batch) operation; for example, a module may be treated separately if only that module has been changed since the last edit-compile-link-run cycle. This level of incremental operation is known as coarse-grained incremental operation.